The menopause marks a period of critical change in women's biology and health. Establishing a staging system for reproductive aging would enable providers to better counsel women about menopausal symptoms and preventive therapy and permit researchers to accurately classify women's reproductive status. The Stages of Reproductive Aging Workshop (STRAW) proposed such a staging system. STRAW'S recommendations, although based on emerging results of ongoing cohort studies, were not data driven and included important departures from clinical and research practice. ReSTAGE is a collaboration among four large cohort studies of the menopausal transition (TREMIN, Melbourne Women's Midlife Health Project, Seattle Midlife Women's Health Study, Study of Women's Health Across the Nation). Our goal has been to empirically evaluate bleeding criteria for the menopausal transition that were the basis for STRAW'S recommendations using menstrual calendars, hormones and symptom data. The original grant focused only on the natural history of the menopausal transition. This competitive renewal addresses three methodological issues critical to specifying inclusive staging criteria broadly applicable to a heterogeneous population of women. It will extend staging criteria to include women who use hormones (HT) during the midlife, address misclassification associated with intermenstrual bleeding/spotting (1MB), and characterize the problem of left truncation and left censoring biases in studies of the menopausal transition. We aim first to develop and compare two approaches for modifying bleeding criteria for the menopausal transition to account for the case where women use HT and assess the effect of including HT users on estimates of age and duration of the menopausal transition in the four cohort studies. Second, as 1MB makes assessment of bleeding criteria difficult, we aim to develop an algorithm for distinguishing 1MB from menstrual episodes in menstrual calendars and to assess IMB's impact on estimates of age at and duration of the transition in the four cohorts. Third, we aim to develop likelihood methods to correct for left censoring and left truncation biases associated with the differential age at entry criteria in cohort studies of midlife women and assess the impact of these biases on estimates of age at and duration of the menopausal transition. This research will extend staging systems for reproductive aging to include HT users and provide definitive guidance regarding criteria for staging reproductive aging in HT users and women with 1MB. Results will facilitate clinical decision making for women and providers relevant to contraception, symptomatic treatment and preventive therapy.